The More Users Online, the Slower the Internet
This is a simplification that distracts from real issues of internet quality. More people online can create internet slowdowns, but this doesn’t have to happen, and with well-built internet infrastructure, it’s usually not a problem. But how local internet infrastructure manages spikes in traffic can vary significantly across the United States. Some networks won’t have a problem, some will have only minor issues, and some will have horrible performance if traffic spikes above a certain level.
Again, a lot of this depends on local activity and specific servers, not how many internet users are online around the entire country. The internet is designed to be as flexible as possible on the whole: A great example is the jump in internet activity from COVID-19 lockdowns. Internet activity rose significantly (by around 20%) and stayed there for months, but most users didn’t notice a slowdown during this time.
Inside your house, the rules are a bit different – the more users that are on a single connection can make a big difference, because of the limited bandwidth you have – but modern multi-band routers with smart allocation can help address these problems.